US6660644B2 - Plasma etching methods - Google Patents

Abstract

A plasma etching method includes forming polymer material over at least some internal surfaces of a plasma etch chamber and forming polymer material over at least some surfaces of a semiconductor wafer received within the plasma etch chamber. Substantially all polymer material is plasma etched from the chamber internal surfaces while at least some polymer material remains on the wafer. In another aspect, a semiconductor wafer is positioned on a wafer receiver within a plasma etch chamber. A photoresist layer has previously been formed thereon and has openings formed therethrough. First plasma etching is conducted through openings formed in the photoresist layer with a gas comprising carbon and a halogen to form openings in material on the wafer. A first polymer comprising carbon and the halogen forms over at least some internal surfaces of the plasma etch chamber during the first plasma etching. A second polymer is formed over the wafer and relative to the material openings to mask said material within the openings. After forming the first and second polymers and with the wafer in the chamber, substantially all the first polymer from chamber internal surfaces is plasma etched while the second polymer masks the material within the openings.

Description

RELATED PATENT DATA

This patent resulted from a continuation application of U.S. patent application Ser. No. 09/429,880, filed Oct. 29, 1999, entitled “Plasma Etching Method”, naming Kevin G. Donohoe and Richard L. Stocks as inventors, the disclosure of which is incorporated by reference, which application resulted from a divisional application of U.S. patent application Ser. No. 09/022,813, filed Feb. 12, 1998, entitled “Plasma Etching Methods”, naming Kevin G. Donohoe and Richard L. Stocks as inventors, now U.S. Pat. No. 6,093,655, issued Jul. 25, 2000, the disclosure of which is incorporated by reference.

TECHNICAL FIELD

This invention relates to plasma etching methods.

BACKGROUND OF THE INVENTION

Plasma etchers are commonly used in semiconductor wafer processing for fabrication of contact openings through insulating layers. A photoresist layer having contact opening patterns formed therethrough is typically formed over an insulative oxide layer, such as SiO₂and doped SiO₂. An oxide etching gas, for example CF₄, is provided within the etcher and a plasma generated therefrom over the wafer or wafers being processed. The etching gas chemistry in combination with the plasma is ideally chosen to be highly selective to etch the insulating material through the photoresist openings in a highly anisotropic manner without appreciably etching the photoresist itself. A greater degree of anisotropy is typically obtained with such dry plasma etchings of contact openings than would otherwise occur with wet etching techniques.

One type of plasma etcher includes inductively coupled etching reactors. Such typically include an inductive plasma generating source coiled about or at the top of the reactor chamber and an electrostatic chuck within the chamber atop which one or more wafers being processed lies. The electrostatic chuck can be selectively biased as determined by the operator. Unfortunately when utilizing etching components having both carbon and fluorine, particularly in inductively coupled etching reactors, a polymer develops over much of the internal reactor sidewall surfaces. This polymer is electrically insulative and continually grows in thickness during the wafer etching process. In addition, the polymer can react with species in the plasma and cause process results to vary as the polymer thickness changes. For an etch 2 microns deep on the wafer, the polymer thickness on certain internal reactor surfaces can be 3000 Angstroms to 6000 Angstroms. It is highly desirable to remove this polymer because it can make process results vary and can contribute to particle contamination of the wafer(s) being processed.

The typical prior art process for cleaning this polymer material from the reactor employs a plasma etch utilizing O₂as the etching gas. It is desirable that this clean occur at the conclusion of etching of the wafer while the wafer or wafers remain in situ within the reactor chamber. This both protects the electrostatic chuck (which is sensitive to particulate contamination) during the clean etch, and also maximizes throughput of the wafers being processed. An added benefit is obtained in that the oxygen plasma generated during the clean also has the effect of stripping the photoresist from over the previously etched wafer.

One prior art plasma clean is conducted in three steps when using a LAM 9100 type inductively coupled plasma etcher. In a first plasma cleaning step, top electrode power is provided at 600 Watts and the bottom at 200 Watts. O₂feed is provided at 750 sccm for 15 seconds, with pressure being maintained at 15 mTorr. In the second step, top power is at 1750 Watts, bottom electrode is not biased (0 Watts), and O₂feed is provided at 500 sccm for 20 seconds with pressure being maintained at 80 mTorr. In a third step, the pins of the electrostatic chuck are raised to lift the wafer(s), and the top power is provided at 1200 Watts, bottom electrode is not biased (0 Watts), and O₂feed is provided at 500 sccm for 15 seconds with pressure being maintained at 80 mTorr.

However in the process of doing reactor clean etches, there is an approximate 0.025 micron or greater loss in the lateral direction of the contact. In other words, the contact openings within the insulating layer are effectively widened from the opening dimensions as initially formed. This results in an inherent increase in the critical dimension of the circuitry design. As contact openings become smaller, it is not expected that the photolithography processing will be able to adjust in further increments of size to compensate for this critical dimension loss.

Accordingly, it would be desirable to develop plasma etching methods which can be used to minimize critical dimension loss of contact openings, and/or achieve suitable reactor cleaning to remove the polymer from the internal surfaces of the etching chamber. Although the invention was motivated from this perspective, the artisan will appreciate other possible uses, with the invention only be limited by the accompanying claims appropriately interpreted in accordance with the Doctrine of Equivalents.

SUMMARY OF THE INVENTION

In but one aspect of the invention, a plasma etching method includes forming polymer material over at least some internal surfaces of a plasma etch chamber and forming polymer material over at least some surfaces of a semiconductor wafer received within the plasma etch chamber. Substantially all polymer material is plasma etched from the chamber internal surfaces while at least some polymer material remains on the wafer.

In another implementation, a semiconductor wafer is positioned on a wafer receiver within a plasma etch chamber. A photoresist layer has previously been formed thereon and has openings formed therethrough. First plasma etching is conducted through openings formed in the photoresist layer with a gas comprising carbon and a halogen to form openings in material on the wafer. A first polymer comprising carbon and the halogen forms over at least some internal surfaces of the plasma etch chamber during the first plasma etching. A second polymer is formed over the wafer and relative to the material openings to mask said material within the openings. After forming the first and second polymers and with the wafer in the chamber, substantially all the first polymer from chamber internal surfaces is plasma etched while the second polymer masks the material within the openings.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below with reference to the following accompanying drawings.

FIG. 1 is a diagrammatic view of a plasma etcher utilized at one processing step in accordance with the invention.

FIG. 2 is an enlarged view of a fragment of a wafer during processing within the plasma etcher of FIG.1.

FIG. 3 is a view of the FIG. 2 wafer at a processing step subsequent to that depicted by FIG.2.

FIG. 4 is a view of the FIG. 1 apparatus and wafer at a processing step subsequent to that depicted by FIGS. 1 and 3.

FIG. 5 is a view of the FIG. 2 wafer at a processing step subsequent to that depicted by FIG.3.

FIG. 6 is a view of the FIG. 2 wafer at a processing step subsequent to that depicted by FIG.5.

FIG. 7 is a view of a fragment of a wafer during processing within the plasma etch of FIG.1 and is an alternate to that depicted by FIG.3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of the constitutional purposes of the U.S. Patent Laws “to promote the progress of science and useful arts” (Article 1, Section 8).

It has been discovered that the polymer deposited on the internal walls of the etching chamber includes a significant concentration of fluorine. It has been recognized that the oxygen during the clean etching under plasma condition combines with the carbon and fluorine of the polymer liberated from the internal walls and forms carbon monoxide and carbon dioxide plus an activated or reactive fluorine containing species. Unfortunately, this fluorine containing species is also apparently reactive with the silicon dioxide material on the wafer, which is believed to result in more etching of such material and the widening of the contact openings.

Some of this polymer also gets deposited on the wafer during the etch. The polymer can deposit over the sidewalls within the etched openings to a thickness of about 200 Angstroms, being thicker over central portions of the sidewalls than at the base or top of the etched openings. The polymer can also deposit on the bottom of the contact during the overetch. Polymer thicknesses of up to 1500 Angstroms have been observed on the bottom of the contact. Presence of this polymer within the contact openings and its removal during subsequent oxide clean etching can also contribute to critical dimension loss. It has, however, been determined that polymer presence over the internal reactor surfaces is a greater contributing factor to critical dimension loss than polymer presence within the contact openings.

Referring to FIG. 1, a plasma etching reactor is indicated generally with references numeral10. Such includes achamber12 havinginternal surfaces14. One ormore gas inlets16 and one ormore gas outlets18 are provided relative toetching chamber12. Apump20 is associated withoutlet18 for exhausting and establishing desired sub-atmospheric pressure conditions withinchamber12 during processing.

Plasma etching reactor10 in the described embodiment is configured as an inductively coupled plasma etcher having awafer receiver22 withinchamber12 in the form of an electrostatic chuck. A biasingsource24 is electrically coupled withreceiver22. An inductiveplasma inducing source26 is diagrammatically shown externally at the top ofchamber12.

In accordance with the preferred embodiment, asemiconductor wafer30 is positioned uponwafer receiver22 withinchamber12.Wafer30 has previously been processed to have aphotoresist layer32 formed on an insulative oxide layer31 (FIG. 2) formed on the outer surface ofwafer30.Photoresist layer32 has contact opening patterns formed therethrough which ideally outwardly expose selected portions of underlyinginsulative oxide layer31. A desired vacuum pressure is established and maintained withinchamber12 utilizingvacuum pump20. An example chamber pressure is from about 2 mTorr to about 200 mTorr. Inductively coupledsource26 and chuck22 are appropriately biased to enable establishment of a desired plasma within and immediately overwafer30. An example power range for inductively coupledsource26 is from 100 watts to about 2000 watts, withwafer receiver22 being negatively biased to an example of −200 to −600 Watts.Receiver22 can have a temperature which is allowed to float, or otherwise be established and maintained at some range, for example from about 0° C. to about 40° C.

Desired etching gases are injected to withinchamber12 throughinlet16, or other inlets, to provide a desired etching gas from which an etching plasma is formed immediately overwafer30. Such gas can comprise, for example, carbon and a halogen. An exemplary gas would be CF₄. Etching is conducted for a selected time to etch desired contact openings, with onesuch opening33 being shown in FIG. 2, withininsulative oxide material31 onsemiconductor wafer30 through the contact opening patterns formed within thephotoresist layer32. Unfortunately, apolymer layer40 comprising carbon and the halogen, and in this example fluorine, forms over some ofinternal surfaces14 ofplasma etching chamber12 during such etching. Such polymer can also form on the top of photoresist layer32 (not specifically shown), with somepolymer material40 also forming over sidewalls within, and at the base of,contact openings33.

Such provides but one example of forming polymer material, alternately referred to as a first polymer, comprising carbon and a halogen over at least some internal surfaces of a plasma etch chamber. Where a 2 micron deep contact opening is being etched withininsulative material31, an exemplary average thickness ofpolymer material40 formed overinternal surfaces14 is 3000 Angstroms. An exemplary maximum thickness oflayer40 formed withincontact openings33 is 200 Angstroms. An exemplary maximum thickness of the polymer deposition on the bottom of the contact is 1000 Angstroms. Thus, a thicker layer of the first polymer forms over internal surfaces of the chamber than over the semiconductor wafer.

Referring to FIG. 3, asecond polymer44 is formed overfirst polymer40 over the wafer and relative tomaterial opening33 tomask material31 withinopening33. In the illustrated example,second polymer layer44 is formed to bridge across opening33 and less than completely fillopenings33.Second polymer layer44 is formed to a greater thickness overwafer30 than any thickness of the second polymer which forms overinternal surfaces14 ofchamber12. Specifically,plasma etching chamber12 can be utilized to deposit polymer material, for example, when using the same etching gases by biasingelectrostatic chuck22 at 0 Watts during gas feed. In such instances, almost no second polymer material forms oninternal surfaces14 ofchamber12, with deposition of second polymer material being essentially selective to the wafer. As biasing power would be applied and increased relative towafer receiver22, second polymer material would begin to deposit overinternal surfaces14 ofchamber12 as a function of increasing bias. Regardless, most preferably the step of forming a second polymer forms such material to a thickness of from 0 Angstroms to no greater than about 100 Angstroms on theinternal surfaces14 ofchamber12. A preferred thickness forlayer44 onwafer30 is greater than or equal to about 3000 Angstroms.

First andsecond polymer materials40 and44 can comprise the same substantial material, or substantially different materials. Where the etching gases and deposition gases are the same, with different biasing power being provided on the wafer receiver, the polymer materials oflayers40 and44 comprise similar fluorocarbon polymers. When constituting similar materials, or materials having essentially the same etching rate in a subsequent etching step, the thickness ofpolymer layer44 is ideally provided to be greater than the average thickness of all polymer material formed overinternal surfaces14. This allows or enables the polymer to be substantially removed fromsurfaces14 before the polymer on the wafer is removed. Wheresecond polymer layer44 is formed to not contain any fluorine, a possible advantage may be obtained in there being no available fluorine in thefinal layer44 strip to potentially widen the contact openings. An example would be a hydrocarbon polymer.

Referring to FIGS. 4 and 5, substantially allpolymer material40/44 is plasma etched from chamberinternal surfaces14 while at least somepolymer material40/44 remains overwafer30, ideally over and within contact opening33 tomask material31 withinopenings33 to prevent such openings from widening during the chamber clean etching.

Referring to FIG. 6, further clean etching is ideally conducted to remove all remaining polymer material of layer(s)44/40 from withincontact opening33, and also to remove any remaining photoresist.

Preferably, the plasma etching of substantially all the first polymer from chamber internal surfaces is conducted in at least four steps comprising at least two different magnitudes of power. Anexample etching reactor10 is an LAM 9100 TCP Etcher. An exemplary preferred first step using such a reactor is to provide zero bias on the wafer receiver and 500 watts from the inductive source. Preferred etching gas flow rate is 750 sccm of O₂for 15 seconds at a pressure of 15 mTorr, with Capacitor4 of the reactor being held at minimum value (approximately 100 pf in the LAM 9100 TCP Etcher). In a second step, all conditions are ideally maintained as with the first step with Capacitor4 being held at 150 pf. A third step is then conducted under the same conditions, except with Capacitor4 being held at a 190 pf. These three steps effectively provide a good clean of the internal reactor surfaces, with the low power being preferred to remove the polymer slowly in a manner which does not remove polymer from the wafer at a rate greater than that being removed from the internal surfaces of the chamber.

A preferred fourth step is then to increase power to 1750 watts on the inductive source, while still providing zero voltage bias on the receiver. An exemplary flow rate during such etching is 500 sccm for O₂for 15 seconds at a pressure of 80 mTorr. Capacitor4 is preferably kept at 100 pf. This etching step is intended to finish the chamber clean. A fifth step is then preferably conducted the same as the fourth, except with Capacitor4 being set to 150 pf. A preferred final etching step is then conducted at a top inductive power of 500 watts, with the wafer receiver being biased at 250 Watts. O₂flow is preferably 750 sccm for 10 seconds with pressure being maintained at 15 mTorr. Capacitor4 is set to 150 pf. Such preferred etching is believed to finally clean out any remnant polymer from within the contacts. With such preferred processing with a LAM 9100 TCP Etcher, a power setting with capacitor4 at a maximum provides greater so cleaning at the center of the chamber. A minimum capacitor setting provides greater cleaning towards the outer portions of the chamber. A balanced power setting for capacitor4 (i.e., 150 pf) provides greater removal in between the outer and inner portions of the chamber.

FIG. 7 illustrates an alternate embodiment relative to that depicted by FIG. 3, wherebysecond polymer layer44ais deposited to completely fillcontact opening33. Alternately but less preferred, the second deposited polymer layer could be conformal to less than completely fillcontact openings33 and not bridge such contact openings shut.

Where the first and second (or additional) polymers are substantially different from one another in etch rate, selectivity in the polymer etching can be used substantially independent of total polymer thickness between that on the chamber walls and that on the wafer.

In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.

Claims (20)

What is claimed is:

1. A plasma etching method comprising:

forming a first polymer over at least some internal surfaces of a plasma etch chamber and over at least some surfaces of a semiconductor wafer received within the plasma etch chamber while plasma etching an oxide layer received on the semiconductor wafer;

after forming the first polymer and after said plasma etching of the oxide layer, forming a second polymer over the first polymer and over the semiconductor wafer without etching said oxide layer and without etching any other material received on the wafer; and

after said formings and with the semiconductor wafer within the chamber, plasma etching substantially all polymer from the chamber internal surfaces while at least some first or second polymer remains on the wafer.

2. The plasma etching method ofclaim 1 wherein the first and second polymers are the same materials.

3. The plasma etching method ofclaim 1 wherein the first and second polymers are different materials.

4. The plasma etching method ofclaim 1 wherein the first polymer is formed with a fluorine comprising feed gas and the second polymer is not formed with a fluorine comprising feed gas.

5. The plasma etching method ofclaim 1 wherein the plasma etching of the oxide layer forms material openings therein, and wherein the second polymer is formed to less than completely fill the material openings.

6. The plasma etching method ofclaim 1 wherein the plasma etching of the oxide layer forms material openings therein, and wherein the second polymer is formed to completely fill the material openings.

7. The plasma etching method ofclaim 1 wherein the plasma etching of the oxide layer while forming the first polymer is completely through said oxide layer to a different material therebeneath.

8. The plasma etching method ofclaim 1 wherein the plasma etching of the oxide layer while forming the first polymer is completely through said oxide layer to a different material therebeneath, and forming the first polymer to be received over and contacting said different material at conclusion of said plasma etching of the oxide layer.

9. A plasma etching method comprising:

forming a first polymer over at least some internal surfaces of a plasma etch chamber and over at least some surfaces of a semiconductor wafer received within the plasma etch chamber while plasma etching an oxide layer received on the semiconductor wafer;

after forming the first polymer and after said plasma etching of the oxide layer, forming a second polymer over the first polymer and over the semiconductor wafer;

after said formings and with the semiconductor wafer within the chamber, plasma etching substantially all polymer from the chamber internal surfaces while at least some first or second polymer remains on the wafer; and

wherein the plasma etching of the oxide layer forms material openings therein, and wherein the second polymer is formed to be bridging across the material openings to less than completely fill the material openings; and

after forming the second polymer to be bridging, etching the second polymer to remove all briding.

10. A plasma etching method comprising:

forming a first polymer over at least some internal surfaces of a plasma etch chamber and over at least some surfaces of a semiconductor wafer received within the plasma etch chamber while plasma etching an oxide layer received on the semiconductor wafer;

after forming the first polymer and after said plasma etching of the oxide layer, forming a second polymer over the first polymer and over the semiconductor wafer;

after said formings and with the semiconductor wafer within the chamber, plasma etching substantially all polymer from the chamber internal surfaces while at least some first or second polymer remains on the wafer; and

wherein the plasma etching of the oxide layer forms material openings therein, and wherein after plasma etching substantially all polymer from the chamber internal surfaces at least some of the second polymer remains on the wafer and to be bridging across the material openings to less than completely fill the material openings; and

after forming the second polymer to be bridging, etching the second polymer to remove all said bridging.

11. A plasma etching method comprising:

forming a first polymer over at least some internal surfaces of a plasma etch chamber and forming a second polymer over at least some surfaces of a semiconductor wafer received within the plasma etch chamber, the first and second polymers constituting different materials, the first polymer being formed while plasma etching openings in material received on the semiconductor wafer, the second polymer being formed while not etching any material received on the wafer; and

after forming the first and second polymers, after said plasma etching of the openings and with the wafer in the chamber, plasma etching substantially all the first polymer from the chamber internal surfaces while at least some first or second polymer remains on the wafer.

12. The plasma etching method ofclaim 11 wherein the first polymer is formed with a fluorine comprising feed gas and the second polymer is not formed with a fluorine comprising feed gas.

13. The plasma etching method ofclaim 11 wherein all of the first polymer formed over the internal surfaces has an average first thickness and all of the second polymer formed over the wafer has an average second thickness, the average thickness of the second polymer being greater than the average thickness of the first polymer.

14. The plasma etching method ofclaim 11 wherein the first polymer is formed over the wafer and has an average first thickness thereover, and wherein the second polymer has an average second thickness on the wafer, the average second thickness being greater than the average first thickness.

15. The plasma etching method ofclaim 11 wherein the second polymer is formed over at least some internal surfaces of the plasma etch chamber, and wherein the second polymer is formed to a greater thickness over the wafer than over the internal surfaces of the plasma etch chamber.

16. The plasma etching method ofclaim 11 wherein the second polymer is formed to less than completely fill the material openings.

17. The plasma etching method ofclaim 11 wherein the second polymer is formed to completely fill the material openings.

18. The plasma etching method ofclaim 11 wherein the plasma etching of the openings while forming the first polymer is completely through a first material to a different second material therebeneath.

19. The plasma etching method ofclaim 11 wherein the plasma etching of the openings while forming the first polymer is completely through a first material to a different second material therebeneath, and forming the first polymer to be received over and contacting said different second material at conclusion of said plasma etching of the openings.

20. A plasma etching method comprising:

forming a first polymer over at least some internal surfaces of a plasma etch chamber and forming a second polymer over at least some surfaces of a semiconductor wafer received within the plasma etch chamber, the first and second polymers constituting different materials, the first polymer being formed while plasma etching openings in material received on the semiconductor wafer;

after forming the first and second polymers, after said plasma etching of the openings and with the wafer in the chamber, plasma etching substantially all the first polymer from the chamber internal surfaces while at least some first or second polymer remains on the wafer; and

wherein after plasma etching substantially all polymer from the chamber internal surfaces at least some of the second polymer remains on the wafer and to be bridging across the material openings to less than completely fill the material openings; and

after forming the second polymer to be bridging, etching the second polymer to remove all said bridging.

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